106 TETHANDRIA TETRAGYNIA. [CL. IV. 



in May : grows in bushy places : frequent. EH*. But. vol. vii. pi. 496. 

 Eng. Fl. vol. i. p. 228. 263. 



17. POTAMOGETON. POWD-WEED. 



Calyx none. Corolla inferior, of four roundish equal petals, 

 furnished with a claw. Filaments very short, flat; anthers ob- 

 long, two-lobed. Germens four, superior, egg-shaped, acute. Style 

 none ; stigmas obtuse, permanent. Seeds four, roundish, bulging 

 on one side, flattened on the other. Named from potamos, a 

 river, and geiton, a neighbour. 80. 



1. P. niltam. Broad-leaved Pond-weed. Upper leaves between ob- 

 long and egg-shaped, stalked, leathery, floating ; lower leaves linear, 



membranous, sessile. Stem round, much branched : upper leaves 



brownish-green : spikes simple, raised above the water : the floating 

 leaves afford an agreeable shade to fish, and the roots are a favourite food 

 of swans. Perennial: flowers in July and August: grows in pools, 

 ditches, canals, and rivers: common. Eng. Bot. vol. xxvi. pi. 1822. 

 Eng. Fl. vol. i. p. 229. 264. 



2. P.heterophyl'lus. Various- leaved Pond-weed. Upper leaves elliptical, 

 stalked, slightly leathery, floating ; lower leaves lance-shaped, membra- 

 nous, sessile. Smaller than the last : upper leaves thinner : flower- 

 stalks enlarged upwards : spikes dense. Perennial : flowers in July and 

 August : grows in pools, ditches, canals, and rivers : common. Eng. 

 Bot. vol. xviii. pi. 1285. Eng. Fl. vol.i. p. 229. 265. 



3. P. rufescens. Long-leaved, Floating Pond-weed. Upper leaves be- 

 tween egg-shaped and lance-shaped, stalked, leathery, floating ; lower 



leaves lance-shaped, membranous, sessile. Upper leaves less leathery, 



olive-coloured or reddish. Perennial: flowers in July and August: 

 grows in ditches, ponds, and slow rivers. Eng. Bot. vol. xviii. pi. 1286. 

 Eng. Fl. vol. i. p. 231. P.fluitans. 266. 



4. P. perfoliiitus. Perfoliute Pond-weed. Leaves heart-shaped, em- 

 bracing the stem, uniform, all submersed. Leaves all sessile, uniform, 



very pellucid, olive-coloured. Perennial : flowers in July and August: 

 grows in slow rivers and ponds : common. Eng. Bot. vol. iii. pi. 168. 

 Eng. Fl. vol. i. p. 230. 267. 



5. P.densus. Close-leaved Pond-weed. Leaves opposite, egg-shaped, 



tapering to a point, crowded ; stem forked ; spike four-flowered. 



Fruit-stalk very short, in the fork of the stem : all the leaves are sub- 

 mersed, and very close together. Perennial : flowers in July and Au- 

 gust : grows in ditches, ponds, and slow rivers : common. Eng. Bot. 

 vol. vi. pi. 397. Eng. Fl. vol. i. p. 231. 268. 



6. P. lucent. Shining Pond-weed. Leaves between elliptical and 

 lance-shaped, pointed, stalked, membranous, sessile; spike dense, many- 

 flowered Leaves large, olive-green, with undulated margins, and 



beautifully veined : spike two inches long, of very numerous, green 

 flowers. Perennial : flowers in June and July : grows in ditches, pond*, 

 lakes, and slow rivers : common. Eng. Bot. vol. vi. pi. 376. Eng. Fl. 

 vol. i. p. 232. 269. 



7. P. preltinguf. Long-stalked Pond-weed. Leaves oblong, obtuse, 

 sessile; peduncles much elongated; spike cylindrical, many-flowered. 



